This invention relates to a synchronous electric motor particularly adapted to supply large power output while maintaining a compact and highly effective construction.
As is well known synchronous motors normally have a rotor and a cooperating stator. The stator comprises coils wound around the respective pole teeth of a stator core. These coils are electrically interconnected in a coil terminal circuit formed on a printed circuit board. A rotation position detector is also provided to detect the rotation angle of the rotor relative to the stator. In household electric appliances, the coil current is usually in the order of several amperes and the coil wire diameter is about 0.3 to 0.6 mm. Various rotation position detector are used such as Hall elements or electric or optical encoders.
There are however other applications for this type of motor that require much greater power output. For example, power assisting synchronous motors are used in the power steering of motor vehicles and/ or in power assisted vehicles such as bicycles, wheelchairs and the like. These applications require a high output and as a result a large current of 20 amperes or more flows through the coils. The coil wire diameter may be about 1 mm or even greater and the coil temperature can rise to as high as about 180 degrees C. in addition, the temperature range over which they operate can vary greatly.
As an example, the coil temperature of a power assisting motor for use such as in the power steering of motor vehicles frequently ranges from −40 to 150 degrees C. and in many instances even greater ranges. Therefore, it is not possible to use a synchronous motor of the same constitution as that of the synchronous motors intended for use in the household electric appliances and specifically using a rotation position detector on which electronic components are mounted. In addition the large currents required cannot be processed simply with coil terminals on a printed circuit board.
A typical prior art construction for higher output motors is shown and described in Japanese patent publication JP-A-Hei06-233483. In this construction the coil windings are connected in phases through conducting members of like ring shape placed one over another for each phase with electrical isolation between them. This assembly is then fixed as a unit at an end surface of the stator. This provides a large current terminal circuit to connect the coil ends.
However with this type of construction the overall assembly the construction becomes complicated and expensive to manufacture. This is because the stator must first be placed in and fixed to a separate casing. Then a separate magnetic pole position detector must be installed and wired. As a result, the overall constitution becomes complicated, the size increases, handling is cumbersome, and assembly and maintenance become more difficult.
It is therefore a principle object of the invention to provide a high power output synchronous motor of a small size, with improved ease of handling, and with compact constitution. It is a further object to provide a single compact unit including a large current terminal circuit and a magnetic pole position detector.